Cloth hanging over a cube but the cloth is floating
Unfortunately Blender's Physics are optimized for mid-scale simulations. Meaning it gets into troubles, when using simulations on a scale &lt; 1m. Roughly.
There is a Thickness outer in the physics tab of your collider, I think that one's default is one of the reasons, but decreasing the value also didn't change much.

If you set your objects to their original scale, the animation works. If 30cm is the exact size you were going for, you'll need to work around that. There are several ways, but too long to explain here.